1. Field of the Invention
This invention relates in general to apparatus for guiding a tape through more than one tape path in a tape recorder; more particularly, the invention is concerned with guides, mounted in a "coaxial-reel" tape cassette, for guiding magnetic tape through more than one tape path, including one path which is so disposed in the tape recorder that a television signal train may be helically recorded on the tape.
2. Description Relative to the Prior Art
While it is not so restricted, the invention acquires a special significance when it is used to guide magnetic tape contained in a coaxial-reel cassette toward and away from a helical recording drum in a video tape recorder. Coaxial-reel cassettes will usually have a pair of inclined or tapered guide posts which are so oriented so as to take up the change in the tape level between the reels when the tape, fully contained in the cassette, passes directly from one reel to the other.
For helical recording, the tape is initially pulled from the cassette and wrapped around the recording drum at a helix angle. In addition, the helical recording format requires precise positioning of the span of tape which passes around the drum; positioning errors may cause, for example, mistracking during playback. Tracking problems are diminished, however, if the tape follows a precise path into, around, and out of the drum assembly. In what has become one frequently used video recorder configuration, the paths into and out of the drum are horizontal and substantially in the same plane as the supply and takeup reels, respectively. The last post before the tape touches the drum and the first post after the tape leaves the drum are designed to change the tape's horizontal level a few degrees so as to dispose the tape properly to form a helix around the drum.
The combination of the coaxial-reel cassette with the helical recorder is hampered significantly because the tape presented to the helical drum is last touched within the cassette by the inclined or tapered guide posts. What this means is that the last guide surfaces within the cassette will tend to force the tape into an inclined path which is not suitable for presentment to the drum assembly and its associated guides. On the other hand, the tape still needs to be positively guided to the vicinity of the drum at the correct height for proper helical scanning. In an attempt to meet this problem, a multiplicity of guides are commonly mounted on the recording deck to positively guide the tape intermediate the cassette and the drum. The guides gradually compensate for the abrupt level change between the coaxial reels and finally present the tape at a suitable angle to the drum assembly. While perhaps expedient for a large machine, the size of such a guiding assembly, as dictated by the length of the tape passing therethrough, limits efforts to reduce the bulkiness of the typical video tape recorder.
Tape guiding configurations have heretofore been proposed which include guiding assemblies within the cassette that provide a tape path favorable to forming a helix around the recording drum when the tape is pulled from the cassette; in addition, such guides still take up the change in the level between the reels when the tape is totally contained inside the cassette. In one such design, several guide pins are provided in one corner of a coaxial cassette -- two obliquely disposed pins and a vertical pin. The tape is directed across the two oblique pins to take up the level change between reels when the tape is totally contained within the cassette. When the tape is drawn out of the cassette, it is first tilted by one oblique pin, rides free of the other oblique pin, and finally is uprighted by the vertical pin, e.g., U.S. Pat. No. 3,800,314. Although the tape may be potentially presented to the drum along a suitable path, the sideways flip-flop of the tape within the cassette can only serve to introduce unwanted distortional transients. Other designs less susceptible to distortion tend to occupy too much space within the cassette. Two cylindrical guides, one canted with respect to the coaxial reels, have been spaced apart in a corner of a cassette, e.g., U.S. Pat. No. 3,672,603. When the tape is withdrawn from the cassette, it rides away from the canted guide and is directed only by the upright guide.
In a somewhat different approach, one configuration proposed includes a spring-loaded guide mounted in a coaxial cassette to transfer tape from one reel to the other, e.g., U.S. Pat. No. 3,678,213. When the cassette is dropped into place on a recorder, a tapered fixed pin mounted on the recorder displaces the spring-loaded guide upward so that magnetic tape riding thereon slides over to the fixed pin. The taper of the fixed pin is such as to alter the direction of tape travel to aid in wrapping the tape around the recording drum. This approach, in effect, provides for the substitution of one guiding surface for another within the cassette. However, this changeover is forced to occur whenever the cassette is placed on the recorder. Such a situation hampers certain operations, such as fast forward or rewind, which may best be accomplished with least damage to the tape by first unwrapping the tape from the drum and letting it wind back into the cassette; than a surface represented by the spring-loaded guide should be in place in order to prevent a buildup of distortional forces on the tape caused by its rapid passage over a surface not suited to the level change between the reels.